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Fa1p is a 171 kDa protein essential for axonemal microtubule severing in Chlamydomonas

Fa1p is a 171 kDa protein essential for axonemal microtubule severing in Chlamydomonas

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  • R. J. Finst
  • P. J. Kim
  • E. R. Griffis
  • L. M. Quarmby

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Original languageEnglish
Pages (from-to)1963-71
Number of pages9
JournalJournal of Cell Science
Issue number11
StatePublished - 2000


A key event in deflagellation or deciliation is the severing of the nine outer-doublet axonemal microtubules at a specific site in the flagellar transition zone. Previous genetic analysis revealed three genes that are essential for deflagellation in Chlamydomonas. We have now identified the first of these products, Fa1p, a protein required for Ca(2+)-dependent, axonemal microtubule severing. Genetic mapping and the availability of a tagged allele allowed us to physically map the gene to the centromere-proximal domain of the mating-type locus. We identified clones of Chlamydomonas genomic DNA that rescued the Ca(2+)-dependent axonemal microtubule severing defect of fa1 mutants. The FA1 cDNA, obtained by RT-PCR, encodes a novel protein of 171 kDa, which is predicted to contain an amino-terminal coiled-coil domain and three Ca(2+)/calmodulin binding domains. By western analysis and subcellular fractionation, the FA1 product is enriched in flagellar-basal body complexes. Based on these observations and previous studies, we hypothesize that a Ca(2+)-activated, Ca(2+)-binding protein binds Fa1p leading ultimately to the activation of axonemal microtubule severing.


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